Welfare at group and individual level: optical flow patterns of broiler chicken flocks are correlated with the behaviour of individual birds

Group level measures of welfare such as the optical flow patterns made by broiler chicken flocks have been criticized on the grounds that they give only average measures and overlook the welfare of individual animals. However, we here show that by using the skew and kurtosis in addition to the mean, optical flow patterns can be used to deliver information not just about the flock average but also about the proportion of individuals in different movement categories. We correlated flock optical flow patterns with the behaviour of a sample of 16 birds per flock in two runway tests and a water (latency-to-lie) test. In the runway tests, there was a positive correlation between the time taken to complete the runway and the skew and kurtosis of optical flow on day 28 of flock life (slow individuals came from flocks with a high skew and kurtosis). In the water test, there was a positive correlation between the length of time the birds remained standing and the mean and variance of flock optical flow (the most mobile individuals came from flocks with the highest mean). Patterns at flock level thus contain valuable information about the welfare of the individuals that compose the flock. Simple SummaryTechnology on farms potentially brings benefits of improved animal health, welfare and productivity as well as reduction in disease, waste and environmental impact. However, it also raises public concern about the welfare of individual animals, particularly when applied to large groups such as broiler (meat) chickens. We here address this issue by showing that camera technology can both provide life-long continuous monitoring of the welfare of whole flocks and also give crucial information about the individuals making up the flock. The cameras detect variation between individuals and are also sensitive to birds moving abnormally. By testing birds individually, we show that slow-moving birds tended to come from flocks that moved slowly overall and showed large variation between individuals whereas fast-moving birds were more likely to come from more active flocks that moved more uniformly. Properly used, camera technology can thus monitor the welfare of flocks continuously throughout their lives while reflecting the behaviour of individual birds.